This project aims to investigate the function of the receptors for granulocyte-macrophage colony stimulating factor (GM-CSF), interleukin-3 (IL-3) and interleukin-5 (IL-5). These factors exert strong proliferative and differentiative effects on myeloid haemopoietic cells. Moreover, autocrine GM-CSF production has been implicated in some leukemias and IL-5 is involved in many allergic reactions, including asthma. The cell-surface receptors for GM-CSF, IL-3 and IL-5 are members of the cytokine receptor family and are comprised of two different subunits, alpha and beta. The alpha-subunit is unique to each factor while the beta- subunit (hbetac) is shared by the three factors. Specifically, it is proposed to utilise a unique set of constitutively active mutants of hbetac to examine the structure, assembly, composition and activity of the functional receptor complexes. These studies will test a model that predicts that hbetac can form intermediate, functional receptor complexes with distinct properties. This studies will be carried out by: (i) Examination of the composition and structure of activated hbetac complexes, in particular those comprising constitutive mutants of hbetac. (ii) Establishing the role of the alpha-subunit in receptor activation. (iii) Examination of the role, in activation and signalling, of molecules associated with the receptor complexes (iv) Examination of the nature and role of cross-activation of EpoR (v) Examination of lipid modification of hbetac and its effects on membrane localisation. In addition, it is proposed that novel reagents (eg. monoclonal antibodies) can be generated which interact with critical regions of hbetac and can trigger signalling activity in the absence of cytokine.